linux-kernel - Re: [PATCH 1/3] gpio / ACPI: add ACPI support

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Date:	Fri, 9 Nov 2012 14:18:21 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-kernel@...r.kernel.org, lenb@...nel.org,
	rafael.j.wysocki@...el.com, broonie@...nsource.wolfsonmicro.com,
	linus.walleij@...aro.org, khali@...ux-fr.org, ben-linux@...ff.org,
	w.sang@...gutronix.de, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/3] gpio / ACPI: add ACPI support

On Fri, Nov 9, 2012 at 2:11 PM, Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
> On 11/08/2012 09:38 PM, Mika Westerberg wrote:
> ...
>
>>>> +#include<linux/errno.h>
>>>> +#include<linux/gpio.h>
>>>> +#include<linux/module.h>
>>>> +#include<linux/acpi_gpio.h>
>>>> +#include<linux/acpi.h>
>>>> +
>>>> +static int acpi_gpiochip_find(struct gpio_chip *gc, void *data)
>>>> +{
>>>> +       acpi_handle handle = data;
>>>> +       acpi_handle gc_handle;
>>>> +
>>>> +       if (!gc->dev)
>>>> +               return false;
>>>> +
>>>> +       gc_handle = gc->dev->acpi_handle;
>>>> +       if (!gc_handle)
>>>> +               return false;
>>>
>>>
>>> This test is redundant with the next one... unless 'handle' is also NULL
>>> :-)
>>>
>>> Is it at all possible for multiple gpiochips to be used for a single
>>> ACPI gpio controller node? Such as if the gpio controller has multiple
>>> banks that should be controlled separately? If so then this won't be
>>> sufficient. I've got the same issue with DT support where the find
>>> function needs to also check if the pin is provided by that specific
>>> gpiochip.
>>
>>
>> AFAIK no but I'll let Mathias to answer that as he knows this better.
>
>
> I'm interpreting it the same way as Mika, max one actual controller per ACPI
> device node
>
> The path (called ResourceSource in ACPI5 specs) in GpioIO/GpioInt resources
> is a "string which uniquely identifies the GPIO controller referred to by
> this descriptor."  The pin number is zero based controller relative.
>
> The  ACPI device controller node includes all other resources needed by the
> controller driver (ioport/mem base, range, interrupt, and Hardware ID used
> to pair with a driver)
>
> Checked a board with two identical gpio controllers on it and it had two
> separate ACPI device node entries. (with only different io address base and
> interrupt resources)

That's not really the situation that I'm thinking about. What I mean
is for a gpio controller that is more convenient for Linux to support
using multiple gpiochips (Linux internal detail), even though there it
is described with a single ACPI node.

g.
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